Combination choke and transformer



Sept. 27, H HARTMANN COMBINATION CHOKE AND TRANSFORMER Filed May 1953 2 Sheets-Sheet l lily.

INVENTOR film BY w joa awwww ATTORNEYS 2 Sheets-Sheet 2 H. HARTMANN COMBINATION CHOKE AND TRANSFORMER Sept. 27, 1955 Filed May 1, 1955 ATTORNEYS R O T N E V m BY M J United States Patent COMBINATION CHOKE AND TRANSFORMER Hans Hartmann, Baden, Switzerland, assignor to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a joint-stock company Application May 1, 1953, Serial No. 352,471

Claims priority, application Switzerland May 2, 1952 1 Claim. (Cl. 336105) The present invention relates to so-called switch choke coils employed in high voltage converters and inverters of the mechanical switching type.

The purpose of the switch choke coil is to widen out or prolong the period during which the current through the switch contacts is approximately zero, i. e. to produce a weak current interval of a given time duration, dt, for spark-free opening of the contacts of a mechanical switch at the end of the current-carrying period of the contacts.

In my prior patent, No. 2,568,003 issued September 18, 1951, there is disclosed and claimed a form of choke wherein the winding thereof consists of two groups of tubular conductors each arranged in coaxial telescoped relation, the conductors being connected electrically in series, and iron cores surrounding and carried respectively by the outer conductor of each group.

The purpose of this invention is to provide an improvement upon the choke shown in that patent and more specifically to structurally combine with the same a transformer for supplying the contacts of the mechanical switch with current to be converted from alternating to direct, or inverted from direct to alternating, as the case may be.

In the improved construction, the winding of the choke also serves as the secondary winding for the transformer, and the primary of the transformer is comprised of a winding wound upon a core which surrounds the conductors of each telescoped conductor group. One advantage of such integration is that it eliminates the need for connecting lines between the choke and transformer.

A structurally combined transformer and choke coil in accordance with the invention also leads to a reduction in ohmic and inductive voltage drops produced due to the heavy currents involved in the conversion and there is also an additional advantage in that less material is required for transformer and choke. Also as eddy current losses are reduced considerably by the arrangement of the invention, this makes for a further improvement in efficiency. Furthermore due to the use of annular cores and tubular conductors the formation of stray fields between structural parts of the organization is greatly reduced.

The foregoing and other objects and advantages of the invention will be apparent from the following specification when taken with the accompanying drawings in which:

Fig. l is a vertical central longitudinal section through a combined choke coil and transformer according to the invention;

Fig. 2 is a transverse section on line 22 of Fig. 1;

Fig. 3 is a view similar to Fig. 1 but somewhat more diagrammatic showing a modified construction for the two physically parallel groups of concentric tubular conductors which make up the winding for the choke coil and transformer secondary; and

Fig. 4 is also a somewhat diagrammatic view in central vertical section of an embodiment similar to Fig. 3

but showing a different arrangement of the cores on the tubular conductors.

With reference now to Figs. 1 and 2 of the drawings, the reference characters al to a8 identify a plurality of tubular conductors arranged in two groups of coaxially telescoped conductors, the axes of the two groups being in parallel physical relation and the conductors of the respective groups being electrically connected to each other in alternation by conductor straps c1 to 07 to form the single series-circuit winding of the choke coil. Sleeves or strips i of insulation are arranged between the telescoped conductors of each group to provide a rigid mechanical assembly of the several parts of the winding.

The innermost conductor al of one group and the outermost conductor a8 of the other group serve as the terminals of the winding. The conductor a1 is preferably extended through an insulator I carried by the cover C of a tank T, for connection into the external circuit network, but the outer conductor a8 can not be similarly extended in view of the conductor straps c2, c4 and 06. A part of the conductor a8 could be cut away to clear the conductor straps but preferably, as shown, the connection to the exterior of the tank T is by way of a connecting strap s and a terminal rod or tube 2 supported in a second insulator bushing'I.

The conductors of each group are preferably stepped or varied in length in order that the connecting straps c1 to c7 may be parallel to each other. Connector c1 joins the lower ends of conductors a1 and a2, and connector 02 connects the upper ends of conductors a2 and a3. In like manner, the remaining connectors are applied to connect the several tubular conductors in series.

Annular cores b1 and b2 for the choke are wound directly upon the outer tubular conductors a7 and a8 of the two groups, and the cores assume the potential of the portions of the conductors to which they are applied. Each core b1 and b2 is preferably formed from strip material preferably a nickel iron alloy wound in spiral form but the cores may be formed in other manners if desired and it will be noted that these cores are arranged on their supporting conductors in the upper portion of tank T.

Below cores b1 and b2 and also on conductors a7 and a8.are arranged two more annular cores el and e2. Each of these cores which are considerably longer in axial direction than cores b1 and b2 can also be made from a spirally wound single sheet but in the illustrated embodiment are seen to be comprised of a plurality of spirally wound strips of relatively short axial length stacked atop one another. The strips are preferably made from a silicon iron alloy. The primary of the transformer consists of one winding section f1 on core el and a second winding section f2 on core e2, and these windings are therefore inductively coupled to the series connected tubular-conductors al to as which also serve as a transformer secondary. The leads to the primary winding can be taken out through the tank cover C in insulator bushings I.

In the illustrated embodiment, the number of turns of the winding for the choke coil are equal to the number of turns for the transformer secondary. However this need not be the case and the number of turns for the transformer secondary may be made less than the number of turns for the choke coil by tapping into the tubular conductors at the desired point and taking a separate lead out through the cover of tank T.

Disks d of insulating material are arranged between the lower ends of the primary windings f1, f2, and the adjacent connecting strap 07, and strips i of insulation are preferably arranged transversely between adjacent pairs of connecting straps to space and strengthen the same. The connecting straps may be of any desired type and,

as illustrated, are in the form of rectangular plates with spaced circular openings into which the ends of a pair of tubular conductors are snugly fitted and soldered or welded.

The lower ends of the innermost conductors a1 and a2 extend into cylindrical openings in a block B of insulation by which the assembly is supported on the bottom wall of tank T, and the lowermost connecting strap or plate 01 rests upon the top of the block. Bores b at the ends of the block communicate with the cylindrical openings into which conductors a1, a2 are stepped to permit circulation of the insulating oil through the tubular conductors for cooling. The upper end of conductor a1 is provided with transverse openings to permit this oil circulation when, as illustrated, the conductor a1 extends to the exterior of tank T.

The number of concentric tubes of each of the parallel groups is in general equal to the number of turns of the choke coil winding as this condition locates the winding terminals on different groups.

The tank T is filled with an insulating oil, not shown, according to current practice, and the insulation i between concentric conductors al to a7 may be provided with longitudinal passageways for thermosyphonic cooling of the winding.

Figs. 3 and 4 illustrate structural modifications wherein the concentric, series connected conductors which serve as the winding for the choke coil and also as the transformer secondary are constituted from a single tubular conductor bent into loop form with at least two turns one within the other as distinguished from the construction shown in Fig. 1 wherein the conductor is made up of two parallel stacks of concentric rectilinear tubes interconnected by straps.

With reference now to Fig. 3 in particular, it will be seen that the conductor is comprised of a first tubular section g2 of a given diameter bent into the general shape of a U and a second tubular section g1 of reduced diameter joined to the end of one leg of the U and which, after being passed through an opening k in the wall of the other leg of tube g2, extends concentrically within the latter around the bottom of the U and emerges from another opening m in the wall of tube g2 near the junction of tubes g1 and g2. It will be understood of course that section g1 of the conductor, to prevent short circuiting with the other conductor section g2, is provided with insulation (not shown) at the pass-through points k and m corresponding in function to the insulation i in the Fig. 1 embodiment. The parallel, upright portions of concentric conductor sections g1 and g2 are surrounded by choke coil cores b3 and b4 and below these cores are the cores e3 and e4 for the transformer primary. The primary windings are f3 and f4 wound on cores e3 and e4, respectively. In this embodiment, conductor section g2 can be considered as one secondary winding connected to phase Ua. of the multi-phase source to be converted and conductor section g1 is another secondary winding connected to a counterphase U of that source. A stub conductor g3 connected with conductor g1 before it enters conductor g2 establishes a center point for the winding and constitutes the star point of the transformer winding connections for the phases.

The arrangement shown in Fig. 4 is similar to that shown in Fig. 3 and differs therefrom only in the fact that core for the choke coil surrounds only the inner conductor g5 and core b6 surrounds only the outer conductor g6. In the Fig. 3 embodiment, the choke coil cores surround both inner and outer conductors.

It is to be understood that the invention is not limited to the particular constructions shown herein and described since variations which may occur to those familiar with the art fall within the spirit and scope of the invention as set forth in the following claim.

I claim:

A combination choke and transformer for use with high current converters with mechanical switching, comprising two groups of coaxially telescoped conductors in parallel physical relation, conductor means interconnecting the conductors of the respective groups to form a plural turn series-circuit winding adapted to serve as a choke coil, first annular iron core means on said conductors forming part of said choke, second annular iron core means on said conductors, and a winding on said second core means constituting a transformer primary, and which is linked with said series-circuit winding, said series circuit winding being tapped intermediate the ends thereof to establish two transformer secondaries, said secondaries surrounding only said second annular iron core means.

References Cited in the file of this patent UNITED STATES PATENTS 2,568,003 Hartmann Sept. 18, 1951 2,655,623 Parker Oct. 13, 1953 FOREIGN PATENTS 617,642 Great Britain Feb. 9, 1949 

